1. Field of the Invention
The present invention relates to a machine frame and particularly but not exclusively, to a frame structure for so-called coordinate measuring machines, comprising at least one first portal which includes two mutually parallel vertical first and second legs which are rotationally and flexurally rigid in relation to a base member and which support a horizontal beam on which a rod or the like which is intended to carry a measuring head, a tool or corresponding device is displaceably mounted. The invention also relates to a method for determining the geometry of the portal determined by deformation of the frame.
2. Description of the Related Art
Coordinate measuring machines are used to measure-up the shape of objects, wherein a large number of points on the object are measured up with regard to their position in a three-dimensional coordinate system, which is defined by the machine. A coordinate measuring machine comprises a measuring head which can be moved in three directions which extend at right angles to one another. The measuring head carries a measuring probe whose position relative to a surface of the object is determined in a coordinate system which is defined by the aforesaid three mutually perpendicular directions. Such coordinate measuring machines are highly accurate in operation and consequently any deformation in the various parts of the machine will influence the measuring result.
Traditionally, efforts have been made to solve this problem by constructing the machine frame from highly rigid and firmly connected components so that any deformations that occur can be ignored. Because of the precision required of such machines in present times, a solution of this nature results in bulky and extremely expensive constructions.
SE-B-468,727 and U.S. Pat. No. 5,119,566 teach other solutions to this problem. These solutions are based on the principle of allowing certain deformations in the machine frame but to construct the frame in a manner which will enable these deformations to be readily calculated and the measuring result corrected on the basis of calculated deformations.
The present invention is also concerned with solving the problem of the effect that deformation of the frame has on the measuring result, by constructing the frame in a manner which will enable deformations to be measured and calculated more easily than in the case of earlier known coordinate measuring machines, so as to enable the measuring result to be corrected in a simple and reliable manner with regard to all deformations that occur, and so that temperature deformations will not induce stresses or force-moments in the construction.